1. Field of the Invention
The present invention relates to a manufacturing method of LED base plate, a LED base plate and a white light LED structure, and in particular relates to a LED base plate providing protrusions with optimized dimension and shape and utilizing ultraviolet light with specific wavelength to scatteringly emit high-brightness white light with an excellent color rendering index.
2. Description of the Related Art
In 1993, Shuji Nakamura, an employee of Nichia Corporation in Japan, applied wide band gap (WGB) semiconductor materials (e.g., GaN and InGaN) to develop blue light LEDs. By incorporating the blue light LEDs with the early-developed red LEDs and green LEDs, various of color light LEDs can be obtained by blending three primary colors, red, green and blue, and in particular white light LEDs can be used for illumination and lighting, to thus cause the rapid development of the LED illumination industries. Taiwan Patent Publication No. 200840096, “METHOD OF PRODUCING GROUP-III NITRIDE SEMICONDUCTOR LAYER, GROUP-III NITRIDE SEMICONDUCTOR LIGHT-EMITTING DEVICE AND LAMP THEREOF”, discloses the skills to enhance the brightness of the LEDs. In '096 case, a method for manufacturing high crystallization group-III nitride semiconductor layer is utilized to provide a production method that enables production of a group-III nitride semiconductor layer having excellent crystallinity which can be used preferably for forming a light-emitting device having excellent internal quantum efficiency and light extraction efficiency. According to '096 case, the production method is a method of producing a group-III nitride semiconductor layer wherein a monocrystal group-III nitride semiconductor is formed on a substrate, the method including: a substrate-processing step where a plurality of projected parts which include a surface which is not parallel to a c-plane of the substrate are formed on the c-plane whereby a top surface which includes a flat surface formed of the c-plane and the projected part are formed on the substrate; and an epi-step where the group-III nitride semiconductor layer is formed on the top surface by epitaxial growth whereby the projected parts are covered with the group-III nitride semiconductor layer. However, the irregular reflection effect of the light on the above-described substrate is determined by the shape and dimension of the projected parts, and the result thereof depends on the brightness of the light scattered from the packaged resin. Herewith, many researchers are devoted themselves on how to optimize the shape and dimension of the projected parts.
Furthermore, Nichia Corporation provides white light LEDs by coating a layer of YAG fluorescent compound on InGaN blue light dies, wherein a yellow light of wavelength 555 nm complementary to the blue light can be generated when utilizing the blue light of wavelength 460 nm to radiate the YAG fluorescent compound, and then a white light can be generated when mixing the yellow light and blue light which are complementary, but the color rendering index of InGaN blue light dies coated with YAG fluorescent compound is not perfect. Accordingly, InGaN ultraviolet light with preferred color rendering index is utilized to generate white light LEDs, but the package layer made of epoxy resin is deteriorated when the package layer is radiated by the very short-wavelength ultraviolet light. Therefore, it is understood that the life span of the white light LED incorporated with ultraviolet light is determined by the selection of the fluorescent compound with respect to the ultraviolet light wavelength.